1. Technical Field
This invention relates to the technologies of collecting, treating, and dispersing exhaust gases from an automotive engine, and more particularly to treatment of such gases with respect to noise suppression and conversion of noxious gaseous elements at or in the location of the engine manifold.
2. Discussion of the Prior Art
Commercially available technology for treating automotive exhaust gases separates the functions of noise suppression, catalytic conversion of noxious gaseous elements, and manifolding to be carried out by independent and separate devices. Firstly, automotive vehicles typically carry a relatively massive muffler device interposed in the tailpipe at a location proximate to the rear of the vehicle. Such muffler has a series of baffles or perforated plates within an expansion chamber which is effective to change the soundwaves, but is also effective to introduce considerable backpressure detracting from fuel economy and engine performance. Secondly, catalytic converters are typically housed in their own canisters interposed in the exhaust system at an underbody location spaced from the engine. Thirdly, manifolds have evolved as direct attachments to engine blocks for collecting exhaust gases from the individual cylinders and are usually made of cast iron to be resistant to the high exhaust gas temperatures leaving the engine exhaust ports.
Within the past several years, some initial effort has been made to combine some of such functions by: (a) use of an insulated chamber at the manifold to promote oxidation; (b) use of a catalyst at or close to the manifold; or (c) use of a muffler at or close to the manifold.
Use of insulated chambers at a manifold to promote oxidation is shown in U.S. Pat. Nos. 3,505,028; 3,581,494; 3,957,446. They illustrate how a shell and insulation is utilized to preserve the temperature of the exhaust gases which, when coupled with the introduction of oxygen, promotes immediate downstream oxidation of hydrocarbons and carbon monoxide. However, this approach has certain disadvantages, including: the lack of a uniform unidirectional flow through the insulated shell avoiding promotion of a high degree of intermixing of the exhaust gases from each of the exhaust ports, the inability to reduce nitric oxides resulting from the introduction of oxygen, the inability to oxidize CO and HC to the extent required by current emission regulations, and the lack of adequate noise suppression. In summary, this approach fails to integrate within one single device a high performing muffler, a manifold that promotes a high degree of intermixing of exhaust gases, and a catalyst that converts substantially all noxious gases. A catalytic converter and a conventional commercially available downstream muffler is still needed to meet existing mandated requirements for exhaust gas treatment.
Close-coupling, only, of catalytic converters to an exhaust manifold is shown in several Japanese and U.S. patents (U.S. Pat. Nos. 4,420,933; 4,663,934; 4,096,691; and 4,151,717; and Japanese 58-2412; 57-210117; 58-72613; 58-107811). None of these references are effective to provide high performing sound suppression; a massive downstream muffler, characteristic of the commercially available prior art, is still necessary to meet this need.
Monolithic catalytic converters, although being potentially effective for high frequency sound suppression, cannot do so without energy wave preparation in advance of the monolith. Thus, in Japanese patents 58-72613; 58-2412; and 56-95455, and U.S. Pat. Nos. 4,420,933 and 4,663,934, the use of diverging flow to the face of the catalytic converter assures that little sound muffling will take place because of the lack of attenuation of high frequency acoustic waves. Conversion efficiency of the latter references is detrimentally affected because of the lack of a streamlined, free-flowing, fully intermixed exhaust gas flow prior to entering the full face of the catalytic converter. U.S. Pat. No. 4,663,934 offers considerable constriction to the flow, preventing it from being free-flowing and promoting significant backpressure. U.S. Pat. Nos. 4,151,717, and 4,096,691 use pellet beds preventing unidirectional flow needed for enhanced conversion efficiency and for sound suppression.
Attempts by the prior art to close-couple a muffler with a manifold are shown in U.S. Pat. Nos. 2,881,851 and 3,419,107. Each uses an expansion chamber, but interrupts the chamber with a series of baffles or perforated plates to promote dissipation of the sound waves, setting up considerable backpressure detracting from fuel economy and engine performance. Moreover, these disclosures lack a high degree of muffling effectiveness because of the added necessity for sound absorbing interior coatings and the need for two exhaust pipes permitting out-of-phase sounds to cancel each other.
What is needed is an integrated device that attains the seemingly contradictory goals of: (a) exhaust flow that is free-flowing with relatively low backpressure to promote enhanced fuel economy and engine performance; (b) noise suppression equal to or better than prior art muffler devices which depend upon flow restrictors; and (c) enhanced catalytic conversion efficiency with uniform distribution of gases over the full frontal area of the catalytic converter. Additionally, it is a goal of this invention to provide flexibility to accommodate curvilinear exhaust flow paths without detrimentally affecting muffler or conversion efficiency.